The present invention relates to a photosensitive imaging material of the type in which a radiation sensitive composition is encapsulated in a plurality of microcapsules and exposure of the composition controls the release of the internal phase from the microcapsules. In the areas in which the internal phase is released an image-forming agent is mobilized and an image is formed. More particularly, the present invention relates to a technique for improving the toe speed of such imaging materials by chemically or physically sequestering a predetermined quantity of the mobilized image-forming agent associated with the capsules.
Photosensitive imaging materials employing encapsulated radiation sensitive compositions are the subject of commonly assigned U.S. Pat. No. 4,399,209 to Sanders et al and U.S. applications Ser. Nos. 320,643 filed Nov. 12, 1981 and 339,917 filed Jan. 18, 1982, as well as Japanese Kokai Nos. 57-124,343 (Aug. 3, 1982) and 57-179836 (Nov. 5, 1982) to Fuji Photo Film Company, Ltd., and Japanese Kokai Nos. 58-17,432 (Feb. 1, 1983) and 58-23,024 (Feb. 10, 1983) to Mitsubishi Paper Mills Corp. In these systems, images are typically formed by reacting a color precursor with a color developer. The color precursor is typically encapsulated with a radiation sensitive composition such as a composition of a polyethylenically unsaturated compound and a photoinitiator.
By image-wise exposing these materials to actinic radiation and rupturing the capsules in the presence of the color developer (which may be on the same support or a separate support from the photoactive microcapsules), the color precursor is image-wise released from the microcapsules and a color image (the reaction product of the color precursor and the color developer) is obtained.
Other imaging systems employing photoactive microcapsules are described in the following patents:
Berman, U.S. Pat. No. 3,219,446 discloses a transfer imaging system in which a blue-black dye is encapsulated with a photocrosslinkable polymer or a photopolymerizable monomer. Images are produced by exposing a layer of the encapsulated material to light and rupturing the capsules in contact with an image-receiving sheet.
Phillips, U.S. Pat. No. 3,700,439, discloses an imaging process in which Michler's ketone is encapsulated and provided as a layer on a support. Irradiation of Michler's ketone converts it to a colorless, acid colorable, dye precursor. Thus, by image-wise exposing the Phillips material to actinic radiation and rupturing the microcapsules in contact with an acid developer layer, a visible image is obtained in the areas in which the ketone is converted to its acid colorable form.
Levy, U.S. Pat. No. 4,149,887, relates to an imaging material in which the microcapsules contain a photoconductive internal phase. By exposing the material in an R.F. field, the conductivity of the internal phase increases so that the microcapsules heat and rupture and thereby release the internal phase which may contain a color precursor which reacts with a developing agent to form an image.
Japanese Kokai, No. 6212/1974 to Matsushiti Denki Sangyo K.K. relates to a recording material in which microcapsules containing a colorless or substantially colorless precursor in a polar solvent are formed with a photocrosslinkable polymer wall material. Images are formed by image-wise exposing the material to actinic radiation to harden the microcapsule walls in the exposed areas, and rupturing the microcapsules in the unexposed areas in contact with a developer material. Thereupon the polar solvent evaporates and a color-producing reaction occurs between the color former and developer.
British Pat. Nos. 1,001,832; 1,058,798; 1,141,475; and 1,193,923 to DuPont disclose an imaging material in which a photopolymerizable substratum contains an ethylenically unsaturated compound. By image-wise exposing the material, the rate of diffusion of an externally applied developer or a color precursor into or out of the photopolymerizable substratum is controlled and images are formed.